This invention relates to a water-drop-proof (hereinafter referred to merely as "drop-proof" when applicable) and dust-proof means in a camera.
A conventional camera is disadvantageous when used in a rainy or dusty environment or in an area exposed to splashing water since the film or even the camera itself may be damaged. Thus, the use of a conventional camera is greatly limited under such conditions.
First, experiments as to how water drops enter a camera will be described with reference to FIGS. 1(a)-1(c), in which reference numeral 1 designates a rotary shaft inserted into a bearing 2, reference numeral 3 designates water drops, and reference numeral 4 designates grease. Referring to FIG. 1(a), when the drops 3 reach the small gap between the rotary shaft 1 and the bearing 2, a so-called capillary effect takes place, and the gap is filled with water as shown. However, because of the water surface tension, the water cannot readily enter the camera and, therefore, the water remains in the gap as shown. When the water entering force overcomes the water surface tension, a so-called "soaking" phenomenon takes place in which the water drops enter the camera. When water drops 3 do not directly strike the gap between the rotary shaft 1 and the bearing 2, the water entering force is substantially determined from the weight of the water only and, thus, it is very weak. In other words, in the arrangement shown in FIG. 1(a), the smaller the gap is (or the closer the fitting tolerance is) and the longer the contact length of the bearing 2 is, the higher will be the soaking prevention effect. Referring to FIG. 1(b), the rotary shaft is relieved at 1b and, therefore, the entering of water drops is stopped by the relief part 1b (because of the water surface tension), and the water-proof effect is correspondingly increased. Referring to FIG. 1(c), the rotary shaft 1 has V-shaped grooves 1c cut therein which are filled with grease 4. Since the water is repelled by the grease 4, the water entering force is weakened and the water-proof effect is increased. The constructions shown in FIGS. 1(a)-1(c) can thus prevent water drops from penetrating the gap between the shaft and bearing, however such arrangements have not proven entirely satisfactory.
Shown in FIG. 2 is a conventional shutter dial section, in which reference numerals 5, 6 and 7 designate an upper decoration board, a shutter dial and an operating rubber ring, respectively, as in FIGS. 1(a)-1(c). Reference numeral 8 designates a decoration ring which is caulked to the upper decoration board 1. With the conventional waterproofing techniques as described above, it is difficult to prevent the entering of rain drops 3 into the camera through the gap between the shutter dial 6 and the decoration ring 8 because the gap is directly exposed to a large amount of water and also because the dial 6 may be slightly eccentric with respect to the ring 8 and rotation of the dial may result in an enlargement of the gap on one side.
FIG. 3 illustrates a functional part of a conventional underwater camera, in which reference numerals 5, 6 and 7 designate an upper decoration board, a shutter dial and an operating rubber ring, respectively, as in FIG. 2. An "O"-ring 9 and an "O"-ring supporting ring 10 are additionally provided for waterproofing. The "O"-ring supporting ring 10 is caulked to the upper decoration board 5, so that the ring 10 and the board 5 form one unit. The viscoelasticity of the "O"-ring 9 prevents rain drops 3 from entering into the camera or prevents water from entering thereinto when the camera is used in the water. Since it is necessary to additionally provide the "O"-ring 9 and the "O"-ring supporting ring 10, the number of components of such a device is increased and, therefore, much labor is required in the assembly of the camera. Furthermore, a space for accommodating the increased number of components is necessary. Accordingly, the sealing method shown in FIG. 3, is not preferable since the recent tendency in manufacturing cameras is to minimize their weights and dimensions.